872 research outputs found
Approximate Reachability for Dead Code Elimination in Esterel*
Esterel is an imperative synchronous programming language for the design of reactive systems. Esterel* extends Esterel with a non-instantaneous jump instruction (compatible with concurrency, preemption, etc.) so as to enable powerful source-to-source program transformations, amenable to formal verification. In this work, we propose an approximate reachability algorithm for Esterel* and use its output to remove dead code. We prove the correctness of our techniques
Dextran sulfate enhances the level of an oxidative DNA damage biomarker, 8-oxo-7,8-dihydro-2'-deoxyguanosine, in rat colonic mucosa.
International audienceDextran sodium sulfate (DSS) given in drinking water can induce colonic inflammation and produce colorectal tumors in rodents, although it is not directly genotoxic. The hypothesis that DSS can produce free radicals and induce oxidative DNA damage in colonic mucosa has been tested. In rats fed for 2 days with water containing 3% and 6% DSS, colonic inflammation manifestations were recorded and 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo), a major biomarker of oxidative DNA damage, was assayed in colonic mucosa. As compared with control rats given pure water, inflammatory manifestations were seen in rats given DSS. At the same time, 8-oxodGuo levels in colonic mucosa were doubled (P < 0.001). These results suggest that formation of oxidative DNA damage in colonic mucosa depends on inflammation and maybe on the production of reactive oxygen species. This study shows that DSS can induce oxidative DNA damage within only 2 days, which could explain in part its carcinogenic properties
Rewriting Logic Semantics of a Plan Execution Language
The Plan Execution Interchange Language (PLEXIL) is a synchronous language
developed by NASA to support autonomous spacecraft operations. In this paper,
we propose a rewriting logic semantics of PLEXIL in Maude, a high-performance
logical engine. The rewriting logic semantics is by itself a formal interpreter
of the language and can be used as a semantic benchmark for the implementation
of PLEXIL executives. The implementation in Maude has the additional benefit of
making available to PLEXIL designers and developers all the formal analysis and
verification tools provided by Maude. The formalization of the PLEXIL semantics
in rewriting logic poses an interesting challenge due to the synchronous nature
of the language and the prioritized rules defining its semantics. To overcome
this difficulty, we propose a general procedure for simulating synchronous set
relations in rewriting logic that is sound and, for deterministic relations,
complete. We also report on two issues at the design level of the original
PLEXIL semantics that were identified with the help of the executable
specification in Maude
Theory of Cylindrical Tubules and Helical Ribbons of Chiral Lipid Membranes
We present a general theory for the equilibrium structure of cylindrical
tubules and helical ribbons of chiral lipid membranes. This theory is based on
a continuum elastic free energy that permits variations in the direction of
molecular tilt and in the curvature of the membrane. The theory shows that the
formation of tubules and helical ribbons is driven by the chirality of the
membrane. Tubules have a first-order transition from a uniform state to a
helically modulated state, with periodic stripes in the tilt direction and
ripples in the curvature. Helical ribbons can be stable structures, or they can
be unstable intermediate states in the formation of tubules.Comment: 43 pages, including 12 postscript figures, uses REVTeX 3.0 and
epsf.st
Non-monotonic variation with salt concentration of the second virial coefficient in protein solutions
The osmotic virial coefficient of globular protein solutions is
calculated as a function of added salt concentration at fixed pH by computer
simulations of the ``primitive model''. The salt and counter-ions as well as a
discrete charge pattern on the protein surface are explicitly incorporated. For
parameters roughly corresponding to lysozyme, we find that first
decreases with added salt concentration up to a threshold concentration, then
increases to a maximum, and then decreases again upon further raising the ionic
strength. Our studies demonstrate that the existence of a discrete charge
pattern on the protein surface profoundly influences the effective interactions
and that non-linear Poisson Boltzmann and Derjaguin-Landau-Verwey-Overbeek
(DLVO) theory fail for large ionic strength. The observed non-monotonicity of
is compared to experiments. Implications for protein crystallization are
discussed.Comment: 43 pages, including 17 figure
SCCharts: Sequentially Constructive Statecharts for Safety-Critical Applications
We present a new visual language, SCCharts, designed for specifying safety-critical reactive systems. SCCharts uses a new statechart notation and provides deterministic concurrency based on a synchronous model of computation (MoC), without restrictions common to previous synchronous MoCs. Specifically, we lift earlier limitations on sequential accesses to shared variables, by leveraging the sequentially constructive MoC. The key features of SCCharts are defined by a very small set of elements, the Core SCCharts, consisting of state machines plus fork/join concurrency. Conversely, Extended SCCharts contain a rich set of advanced features, such as different abort types, signals, history transitions, etc., all of which can be reduced via model-to-model transformations into Core SCCharts. This approach enables a simple yet efficient compilation strategy and aids verification and certification
Equation of state and phonon frequency calculations of diamond at high pressures
The pressure-volume relationship and the zone-center optical phonon frequency
of cubic diamond at pressures up to 600 GPa have been calculated based on
Density Functional Theory within the Local Density Approximation and the
Generalized Gradient Approximation. Three different approaches, viz. a
pseudopotential method applied in the basis of plane waves, an all-electron
method relying on Augmented Plane Waves plus Local Orbitals, and an
intermediate approach implemented in the basis of Projector Augmented Waves
have been used. All these methods and approximations yield consistent results
for the pressure derivative of the bulk modulus and the volume dependence of
the mode Grueneisen parameter of diamond. The results are at variance with
recent precise measurements up to 140 GPa. Possible implications for the
experimental pressure determination based on the ruby luminescence method are
discussed.Comment: 10 pages, 6 figure
Phase equilibria and glass transition in colloidal systems with short-ranged attractive interactions. Application to protein crystallization
We have studied a model of a complex fluid consisting of particles
interacting through a hard core and a short range attractive potential of both
Yukawa and square-well form. Using a hybrid method, including a self-consistent
and quite accurate approximation for the liquid integral equation in the case
of the Yukawa fluid, perturbation theory to evaluate the crystal free energies,
and mode-coupling theory of the glass transition, we determine both the
equilibrium phase diagram of the system and the lines of equilibrium between
the supercooled fluid and the glass phases. For these potentials, we study the
phase diagrams for different values of the potential range, the ratio of the
range of the interaction to the diameter of the repulsive core being the main
control parameter. Our arguments are relevant to a variety of systems, from
dense colloidal systems with depletion forces, through particle gels,
nano-particle aggregation, and globular protein crystallization.Comment: 20 pages, 10 figure
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